This invention relates to a drive system and more particularly to a drive system useful in, among other things, a night vision device for rotating one of a plurality of optical components into an operative position with respect to the night vision device.
Night vision devices include binoculars or monoculars that are used for intensifying low levels of ambient light to enable the user to see in the night. These devices generally include an image intensification tube having an objective lens that receives ambient light which is intensified by the image intensification tube and presented to the user. Night vision devices are well known in the art and may be hand carried or mounted to a helmet or a head mounted harness, worn by the user, to facilitate their use by soldiers in various vehicles or on the ground.
Image intensification tubes are susceptible to interference from laser light and in some cases the tube can be damaged by laser light.
To protect the night vision device from laser light, it is known to use a single laser interference filter that is operatively arranged with the objective lens to protect the image intensification tube from the effects of laser light. See for example U.S. Pat. No. 6,075,661 issued on Jan. 13, 2000 to Ted J. Gross et al. In the Gross patent there is provision for a single laser interference filter that fits over the free end of the objective lens to filter laser light. It has been found that a single laser interference filter is not completely satisfactory and that a filter system including two filters is, in some situations, preferable to protect the image intensification tube. Each of these two filters has a different filtering capability such that one or the other is best used depending on the characteristics of the laser light, e.g., its wavelength or its power density, whether it is continuous or pulsed and other like characteristics. The filters are stowed in an inoperative position in which they are out of the path of the ambient light. When a filter is needed, the desired filter is selected and is driven to an operative position adjacent the objective lens to protect the tube. The other filter is retained in an inoperative position.
Providing a drive system or actuator for moving the selected filter to its operative position can be accomplished by the use of two motors, one for each filter, whereby the selected filter is moved by energizing it associated motor. Such arrangements are rather expensive, bulky and heavy. Accordingly, it is desirable to have an inexpensive, light weight arrangement for actuating the selected filter.